Published online Jul 21, 2014. doi: 10.3748/wjg.v20.i27.9026
Revised: February 11, 2014
Accepted: May 12, 2014
Published online: July 21, 2014
Processing time: 208 Days and 13.3 Hours
Nonalcoholic fatty liver disease (NAFLD), defined as abnormal accumulation (> 5%) of hepatic triglyceride without excess alcohol intake, is the most common form of chronic liver disease in adults and children in the United States. NAFLD encompasses a spectrum of histologic findings including uncomplicated steatosis, steatosis with inflammation and steatohepatitis [nonalcoholic steatohepatitis (NASH)]; the latter can advance to cirrhosis and hepatocellular carcinoma. NASH is currently accepted as the hepatic manifestation of the set of cardiovascular risk factors collectively known as metabolic syndrome. In 1999 a system for histologic grading and staging for NASH was proposed; this was revised by the NASH Clinical Research Network in 2005 for the entire spectrum of lesions in NAFLD, including the lesions and patterns of pediatric NAFLD, and for application in clinical research trials. Diagnosis remains distinct from grade and stage. A recent European proposal separates steatosis from activity to derive a numeric diagnosis of NASH. Even though there have been promising advancements in non-invasive testing, these tests are not yet detailed enough to replace the full range of findings provided by liver biopsy evaluation. Limitations of biopsy are acknowledged, but liver biopsy remains the “gold standard” for diagnosis and determination of amounts of necroinflammatory activity, and location of fibrosis, as well as remodeling of the parenchyma in NASH. This review focuses on the specific histologic lesions of NAFLD and NASH, grading and staging, differential diagnoses to be considered, and the continuing role of the liver biopsy in this important liver disease.
Core tip: Nonalcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease; no clinical or serologic tests have yet replaced liver biopsy for definitive diagnosis. The histologic spectrum includes steatosis, steatohepatitis, and cirrhosis with or without active steatohepatitis. Hepatocellular carcinoma may occur in cirrhosis, or prior to cirrhosis. Liver biopsy provides vital data for patient care, clinical trials, and for ongoing research into nuances of the disease process. The histologic spectrum of NAFLD, features with co-existent diseases, differential diagnoses, grading and staging methods and the role of liver biopsy, as well as a brief description of non-invasive alternatives, are discussed.